Rashi on Exodus 19:22/רש"י על שמות י״ט:כ״ב

1וגם הכהנים AND THE PRIESTS ALSO — the first born sons also, through whom the sacrificial service was carried out (Zevachim 115b),

2‘הנגשים אל ה WHO MAY DRAW NIGH UNTO THE LORD to offer sacrifices — let them also not rely upon their rank and ascend the mountain, but

3יתקדשו LET THEM BE PREPARED to remain at their post,

4פן יפרץ LEST [THE LORD] BURST FORTH — The word פרץ is of the same root and meaning as פרצה “a breach”; the sense is: He may slay some of them and thus cause a breach in their ranks.